Anterior abdominal wall (Figs 5.1-5.8)

The anterior abdominal wall is bounded superiorly by the lower costal margin and inferiorly by the symphysis pubis, the pubic crest and tubercle, the inguinal ligament, the anterior superior iliac spine and the iliac crest, from medial to lateral (Fig. 5.2). The wall comprises three flat sheet-like muscles. They fuse medially to form a fibrous sheath for the vertically running rectus abdominis muscles, lying on each side of the midline. The sheaths of the two sides meet in the midline as a fibrous raphe, known as the linea alba. The three transverse lines of attachment of the rectus abdominis muscle to the anterior sheath can be seen in a muscular subject above the umbilicus; they are termed tendinous intersections (Fig. 5.1). The superior end of the rectus abdominis muscle crosses the anterior rib cage to be attached to the fifth, sixth and seventh costal cartilages from lateral to medial. The lateral line of formation of the rectus sheath is known as the linea semilunaris.

5.1 Anterior abdominal wall

5.2 Anterior abdominal wall: bones

1 Costal margin

2 Xiphisternum

3 Fifth, sixth and seventh costal cartilages

4 Symphysis pubis

5 Body of pubis

6 Pubic tubercle

7 Inguinal ligament

8 Anterior superior iliac spine

9 Iliac crest

10 Iliac tubercle

11 Linea alba

12 Linea semilunaris

13 Rectus abdominis muscle

14 Tendinous intersections

5.3 Anterior abdominal wall: palpable structures

1 Body of sternum

2 Xiphisternum

3 Costal margin

4 Tubercle of ilium

5 Anterior superior iliac spine

6 Upper border of two pubic bones, united by midline symphysis pubis

5.4 Anterior abdominal wall: muscles

1 Anterior superior iliac spine

2 Inguinal ligament

3 Pubic tubercle

4 Superficial inguinal ring

5 External oblique aponeurosis

6 External oblique muscle fibres

7 Tendinous intersections of rectus abdominis

8, 9 Cut edges of external oblique

10 Internal oblique muscle fibres

11 Conjoint tendon

12 Rectus abdominis muscle

5.5 Regions of the abdomen

1 Subcostal plane

2 Transtubercular plane

3 Transpyloric plane

4 Epigastrium

5 Umbilical

6 Suprapubic

7 Hypochondrium

8 Lumbar

9 Iliac

5.6 Surface markings of the alimentary tract

1 Oesophagus

2 Stomach

3 Pyloric antrum

4 Duodenum

5 Duodenojejunal flexure

6 Terminal ileum

7 Caecum

8 Appendix (in pelvic position)

9 Ascending colon

10 Transverse colon

11 Descending colon

12 Sigmoid colon

5.7 Abdomen: plain abdominal radiograph

1 Third lumbar vertebra

2 Ilium

3 Superior ramus of pubis

4 Head of femur

5 Gas shadows in small gut

6 Gas shadows in left colon

7 Gas shadows in rectum

5.8 Surface marking of non-alimentary tract abdominal viscera (The structures labelled 3–6 lie on the posterior abdominal wall)

1 Liver

2 Gall bladder

3 Spleen

4 Pancreas

5 Aortic bifurcation

6 Formation of inferior vena cava

The most superficial of the three sheet-like abdominal muscles is the external oblique; it is attached superiorly by slips to the lateral aspect of the lower eight ribs and interdigitates with the serratus anterior over the middle four ribs. Medially, the muscle forms part of the rectus sheath and inferiorly it is attached to the symphysis pubis, pubic tubercle, anterior superior iliac spine and the anterior half of the iliac crest. The muscle is extensively aponeurotic medial to, and below, a line descending vertically downwards from the ninth costal cartilage to below the level of the umbilicus. The line then curves laterally towards the anterior superior iliac spine. Between the spine and the pubic tubercle, the aponeurotic edge is recurved on itself to form the inguinal ligament. The muscle has a free posterior border but this is not usually visible or palpable in a living subject. The muscles of the anterior abdominal wall are supplied by the lower five intercostal, the subcostal and the first lumbar nerves.

The anterior abdominal wall is divided for descriptive purposes into nine regions by two horizontal lines (subcostal and transtubercular) and two vertical lines through the midpoint of each clavicle (Fig. 5.5 – these lines cross the costal margin at the tip of the ninth costal cartilage and the midinguinal point). The subcostal plane passes through the lower border of the third lumbar vertebra; the transtubercular plane passes through the iliac tubercle and the fifth lumbar spine. The three central regions formed by these lines are the epigastrium, umbilical and suprapubic, from above downwards. The three regions on each side are the hypochondrium, lumbar and iliac, from above downwards. Another plane sometimes referred to in clinical practice is the horizontal, transduodenal (transpyloric) plane, passing through the first part of the duodenum. It is at the level of the lower border of the first lumbar vertebra; ventrally, the transpyloric plane lies midway between the xiphisternal joint and the umbilicus. The abdominal cavity extends upwards behind the lower ribs under the diaphragm and downwards into the pelvis to the pelvic diaphragm (formed by the levator ani muscles).